Alternator overvoltage protection circuit

ABSTRACT

Disclosed is an alternator overvoltage protection circuit having a TRIAC and a MOSFET. The TRIAC is electrically connected to the MOSFET and the TRIAC is electrically connected to a magneto. The TRIAC is configured to ground the magneto when triggered by the MOSFET. The MOSFET is electrically connected to an alternator and configured to conduct when the alternator operates in an overvoltage condition. Also disclosed is a method of alternator overvoltage protection for a piece of outdoor power equipment, the method including providing a TRIAC and an alternator rotated by an engine having a magneto, wherein the alternator outputs a voltage when rotated by the engine. The method further includes configuring the TRIAC to ground the magneto when the alternator operates in an overvoltage condition, thereby disabling the magneto, which stops the rotation of the engine and stops the alternator from outputting voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 61/749,295 filed Jan. 5, 2013 and entitled “ALTERNATOROVERVOLTAGE PROTECTION CIRCUIT”, which is herein incorporated byreference in its entirety. Further, PCT/US14/10237 filed Jan. 3, 2014and entitled “ALTERNATOR OVERVOLTAGE PROTECTION CIRCUIT” is related tothis application and is herein incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The present invention is directed to outdoor power equipment, and moreparticularly to an alternator overvoltage protection circuit for a pieceof outdoor power equipment.

BACKGROUND OF THE INVENTION

Under typical operating conditions, the voltage output of an alternatorin a piece of outdoor power equipment is typically regulated by abattery in the piece of outdoor power equipment. However, an alternatorovervoltage condition, in which the voltage output of the alternatorbecomes excessive, can occur by a sudden loss of connection to thebattery. Further, an alternator overvoltage condition can also occurwhen a piece of outdoor power equipment with a failed or damaged(sulfated) battery is jump started from an external source, and theexternal source, which regulated the alternator when connected, isremoved after the engine is operating.

Therefore, a need exists for an alternator overvoltage protectioncircuit for a piece of outdoor power equipment.

BRIEF SUMMARY OF THE INVENTION

In one aspect of the invention, an alternator overvoltage protectioncircuit comprises a TRIAC and a MOSFET; the TRIAC is electricallyconnected to the MOSFET, the TRIAC is electrically connected to amagneto, wherein the TRIAC is configured to ground the magneto whentriggered by the MOSFET; and the MOSFET is electrically connected to analternator, wherein the MOSFET is configured to conduct when thealternator operates in an overvoltage condition.

In another aspect of the invention, the alternator is connected to androtated by an engine, wherein the magneto is connected to and providesspark to the engine.

In a further aspect of the invention, the alternator provides a voltageoutput; wherein grounding the magneto with the TRIAC disables themagneto and stops the voltage output from the alternator.

In another aspect of the invention, the alternator overvoltageprotection circuit further comprises a transistor; wherein thetransistor is electrically connected to the alternator, wherein thetransistor is configured to conduct when the alternator operates in theovervoltage condition.

In a further aspect of the invention, the overvoltage condition ispresent when the alternator outputs a voltage greater than about 18.65VDC.

In another aspect of the invention, the overvoltage condition is presentwhen the alternator outputs a voltage greater than about 15 VDC.

In a further aspect of the invention, the overvoltage condition ispresent when the alternator outputs a voltage greater than about 20 VDC.

In yet another aspect of an embodiment of the invention, an alternatorovervoltage protection circuit comprises a TRIAC and a MOSFET; the TRIACis electrically connected to the MOSFET, the TRIAC is electricallyconnected to a magneto, wherein the TRIAC is configured to ground themagneto when triggered by the MOSFET; and the MOSFET is electricallyconnectable to an alternator, wherein the MOSFET is configured toconduct when the alternator operates in an overvoltage condition.

In another aspect of the invention, the alternator is connected to androtated by an engine, wherein the magneto is connected to and providesspark to the engine.

In a further aspect of the invention, the alternator provides a voltageoutput; wherein grounding the magneto with the TRIAC disables themagneto and stops the voltage output from the alternator.

In another aspect of the invention, the alternator overvoltageprotection circuit further comprises a transistor; wherein thetransistor is electrically connectable to the alternator, wherein thetransistor is configured to conduct when the alternator operates in theovervoltage condition.

In a further aspect of the invention, the overvoltage condition ispresent when the alternator outputs a voltage greater than about 18.65VDC.

In another aspect of the invention, the overvoltage condition is presentwhen the alternator outputs a voltage greater than about 15 VDC.

In a further aspect of the invention, the overvoltage condition ispresent when the alternator outputs a voltage greater than about 20 VDC.

In yet another aspect of an embodiment of the invention, a method ofalternator overvoltage protection for a piece of outdoor power equipmentcomprises providing a TRIAC and an alternator rotated by an enginehaving a magneto, wherein the alternator outputs a voltage when rotatedby the engine; and configuring the TRIAC to ground the magneto when thealternator operates in an overvoltage condition, thereby disabling themagneto, stopping the rotation of the engine, and stopping thealternator from outputting voltage.

In another aspect of the invention, the method further comprisesproviding a transistor and a MOSFET; configuring the transistor toconduct when the alternator operates in the overvoltage condition;configuring the MOSFET to conduct when a voltage is imposed on a gate ofthe MOSFET by the conducting transistor; and configuring the MOSFET todirect a portion of current from the magneto to trigger a gate of theTRIAC when the MOSFET is conducting, thereby causing the TRIAC toconduct.

In a further aspect of the invention, the overvoltage condition ispresent when the alternator output voltage is greater than about 18.65VDC.

In another aspect of the invention, the overvoltage condition is presentwhen the alternator output voltage is greater than about 15 VDC.

In a further aspect of the invention, the overvoltage condition ispresent when the alternator output voltage is greater than about 20 VDC.

In yet another aspect of an embodiment of the invention, an alternatorovervoltage protection circuit comprises a conditioner section, atrigger section, a drive section, and a disable section; the conditionersection is connectable to an alternator rotated by an engine, and thedisable section is connectable to a load; the trigger section is locatedbetween and electrically connected to the conditioner section and thedrive section; the drive section is located between and electricallyconnected to the trigger section and the disable section; the load is amagneto connected to and configured to supply spark to the engine; theconditioner section is configured to condition voltage output receivedfrom the alternator, and output the conditioned voltage to the triggersection; the trigger section is configured to receive the conditionedvoltage from the conditioner section; the trigger section is furtherconfigured to output current to the drive section when the alternatoroutput voltage exceeds an alternator overvoltage threshold, wherein thetrigger section does not output current to the drive section when thealternator output voltage does not exceed the alternator overvoltagethreshold; the drive section is configured to activate the disablesection when the drive section receives current from the triggersection; and the disable section is configured to divert at least aportion of current away from the magneto to a ground of the alternatorovervoltage protection circuit through a low impedance path when thedisable section is activated, thereby removing spark from and disablingthe engine.

In another aspect of the invention, the disable section comprises adisable TRIAC having a main terminal 1 (MT1) connected to the magnetoand a main terminal 2 (MT2) connected to the ground, wherein the disableTRIAC is configured to conduct when the disable section is activated,thereby creating a first current path between the magneto at the MT1 andthe ground at the MT2.

In a further aspect of the invention, the disable TRIAC is configured totrigger and conduct in quadrant 3.

In another aspect of the invention, the drive section activates thedisable section by creating a low impedance path through the drivesection between the magneto and the ground, the low impedance pathbetween the magneto and the ground creates a second current path and athird current path; the third current path uses a portion of currentprovided by the magneto to produce a voltage at a gate of the disableTRIAC, the second current path removes current from the gate of thedisable TRIAC, thereby causing disable TRIAC to conduct, wherein thevoltage produced at the gate of the disable TRIAC and the currentremoved from the gate of the disable TRIAC are sufficient for thedisable TRIAC to trigger and conduct in quadrant 3.

In a further aspect of the invention, the low impedance path created bythe drive section is comprised of a drive MOSFET; the drive MOSFET isconfigured to transition from a high impedance state to a low impedancestate when the trigger section provides current to the drive section;wherein the current provided from the trigger section to the drivesection flows through a drive voltage divider in the drive section,which produces a voltage at a gate of the drive MOSFET sufficient forthe path between a drain and a source of the drive MOSFET to transitionfrom high impedance state to a low impedance state.

In another aspect of the invention, the drive voltage divider isconfigured to charge a drive capacitor of the drive section, wherein thedrive capacitor is connected to the gate of the drive MOSFET andcontains sufficient charge to maintain the drive MOSFET in the lowimpedance state for a few seconds after the engine stops rotating.

In a further aspect of the invention, the trigger section is comprisedof a trigger transistor configured to receive current from thealternator through the conditioner section, the trigger transistor isfurther configured to provide current to the drive voltage divider whenthe alternator output voltage exceeds the alternator overvoltagethreshold.

In another aspect of the invention, the alternator overvoltage thresholdis about 15 VDC.

In a further aspect of the invention, the alternator overvoltagethreshold is about 18.65 VDC.

In another aspect of the invention, the alternator overvoltage thresholdis about 20 VDC.

In a further aspect of the invention, the conditioner section iscomprised of a conditioner diode, a conditioner resistor, a conditionerzener diode, and a conditioner capacitor; an anode of the conditionerdiode receives the voltage output from the alternator; a first end ofthe conditioner resistor is connected to a cathode of the conditionerdiode and a second end of the conditioner resistor is connected to thetrigger section, the conditioner zener diode and the conditionercapacitor are connected in parallel, a cathode of the conditioner zenerdiode and an anode of the conditioner capacitor are connected to thesecond end of the conditioner resistor; an anode of the conditionerzener diode and a cathode of the conditioner capacitor are connected tothe ground; the trigger section is comprised of a trigger zener diode, atrigger capacitor, a trigger resistor, and a trigger transistor; acathode of the trigger zener diode and a collector of the triggertransistor are connected to a second end of the conditioner resistor,the cathode of the conditioner zener diode, and the anode of theconditioner capacitor; an anode of the trigger zener diode, a first endof the trigger resistor and an anode of the trigger capacitor areconnected; a cathode of the trigger capacitor is connected to theground; a second end of the trigger resistor is connected to a base ofthe trigger transistor; an emitter of the trigger transistor isconnected to the drive section; the drive section is comprised of afirst drive resistor, a second drive resistor, a third drive resistor, adrive capacitor, a drive diode, and a drive MOSFET; a first end of thesecond drive resistor receives current from the emitter of the triggertransistor; a second end of the third drive resistor is connected to theground; a second end of the second drive resistor and a first end of thethird drive resistor are connected; the second drive resistor and thethird drive resistor comprise a drive voltage divider between theemitter of the trigger transistor and the ground; an anode of the drivecapacitor is connected to the second end of the second drive resistor,the first end of the third drive resistor, and a gate of the driveMOSFET; a source of the drive MOSFET is connected to the ground and adrain of the drive MOSFET is connected to a cathode of the drive diode;an anode of drive diode is connected to a second end of the first driveresistor, and a first end of the first drive resistor is connected tothe disable section; and the disable section is comprised of a disableresistor, a disable capacitor, and a disable TRIAC; a second end of thedisable resistor, a cathode of the disable capacitor, and a gate of thedisable TRIAC are connected to the first end of the first driveresistor; a first end of the disable resistor, an anode of the disablecapacitor, and a main terminal 1 (MT1) of the disable TRIAC areconnectable to the magneto; a main terminal 2 (MT2) of the disable TRIACis connected to the ground.

In yet another aspect of an embodiment of the invention, an alternatorovervoltage protection circuit comprises: a conditioner section, atrigger section, a drive section, and a disable section; the conditionersection is connectable to an alternator rotated by an engine, and thedisable section is connectable to a load; the trigger section is locatedbetween and electrically connected to the conditioner section and thedrive section; the drive section is located between and electricallyconnected to the trigger section and the disable section; the load is acoil of an engine component, wherein removal of power from the coil isconfigured to disable the engine; the alternator is configured toprovide power to the coil through a disable resistive element of thedisable section, wherein a second end of the disable resistive elementis connected to a first end of the coil; the conditioner section isconfigured to condition voltage output received from the alternator, andoutput the conditioned voltage to the trigger section; the triggersection is configured to receive the conditioned voltage from theconditioner section; the trigger section is further configured to outputcurrent to the drive section when the alternator output voltage exceedsan alternator overvoltage threshold, wherein the trigger section doesnot output current to the drive section when the alternator outputvoltage does not exceed the alternator overvoltage threshold; the drivesection is configured to activate the disable section when the drivesection receives current from the trigger section; and the disablesection is configured to divert at least a portion of current away fromthe coil to a ground of the alternator overvoltage protection circuitthrough a low impedance path when the disable section is activated,thereby disabling the engine.

In another aspect of the invention, the disable section comprises adisable TRIAC having a main terminal 1 (MT1) connected to the second endof the disable resistive element and a main terminal 2 (MT2) connectedto the ground, wherein the disable TRIAC is configured to conduct whenthe disable section is activated, thereby creating a first current pathbetween the second end of the disable resistive element at the MT1 andthe ground at the MT2.

In a further aspect of the invention, the disable TRIAC is configured totrigger and conduct in quadrant 3.

In another aspect of the invention, the drive section activates thedisable section by creating a low impedance path through the drivesection between the second end of the disable resistive element and theground, the low impedance path between the second end of the disableresistive element and the ground creates a second current path and athird current path; the third current path uses a portion of currentprovided by the disable resistive element to produce a voltage at a gateof the disable TRIAC, the second current path removes current from thegate of the disable TRIAC, thereby causing disable TRIAC to conduct,wherein the voltage produced at the gate of the disable TRIAC and thecurrent removed from the gate of the disable TRIAC are sufficient forthe disable TRIAC to trigger and conduct in quadrant 3.

In a further aspect of the invention, the low impedance path created bythe drive section is comprised of a drive MOSFET; the drive MOSFET isconfigured to transition from a high impedance state to a low impedancestate when the trigger section provides current to the drive section;wherein the current provided from the trigger section to the drivesection flows through a drive voltage divider in the drive section,which produces a voltage at a gate of the drive MOSFET sufficient forthe path between a drain and a source of the drive MOSFET to transitionfrom high impedance state to a low impedance state.

In another aspect of the invention, the drive voltage divider isconfigured to charge a drive capacitor of the drive section, wherein thedrive capacitor is connected to the gate of the drive MOSFET andcontains sufficient charge to maintain the drive MOSFET in the lowimpedance state for a few seconds after the engine stops rotating.

In a further aspect of the invention, the trigger section is comprisedof a trigger transistor configured to receive current from thealternator through the conditioner section, the trigger transistor isfurther configured to provide current to the drive voltage divider whenthe alternator output voltage exceeds the alternator overvoltagethreshold.

In another aspect of the invention, the alternator overvoltage thresholdis about 15 VDC.

In a further aspect of the invention, the alternator overvoltagethreshold is about 18.65 VDC.

In another aspect of the invention, the alternator overvoltage thresholdis about 20 VDC.

In a further aspect of the invention, the disable resistive element iscomprised of a fuse with a current flow rating less than that of theamount of current flowing through the low impedance path when thedisable section is activated, wherein the fuse of the resistive elementis configured blow when the current flows through the low impedance pathupon the activation of the disable section, thereby removing power fromthe coil and disabling the engine.

In another aspect of the invention, the disable resistive element iscomprised of a resistor having a resistance value such that the coildrops out, due to the flow of current through the low impedance path,when the disable section is activated, wherein the dropping out of thecoil disables the engine.

In another aspect of the invention, the coil is a fuel solenoid coil,air intake valve coil, and/or a fuel pump relay coil.

In a further aspect of the invention, the conditioner section iscomprised of a conditioner diode, a conditioner resistor, a conditionerzener diode, and a conditioner capacitor; an anode of the conditionerdiode receives the voltage output from the alternator; a first end ofthe conditioner resistor is connected to a cathode of the conditionerdiode and a second end of the conditioner resistor is connected to thetrigger section, the conditioner zener diode and the conditionercapacitor are connected in parallel, a cathode of the conditioner zenerdiode and an anode of the conditioner capacitor are connected to thesecond end of the conditioner resistor; an anode of conditioner zenerdiode and a cathode of conditioner capacitor are connected to theground; the trigger section is comprised of a trigger zener diode, atrigger capacitor, a trigger resistor, and a trigger transistor; acathode of the trigger zener diode and a collector of the triggertransistor are connected to a second end of the conditioner resistor,the cathode of the conditioner zener diode, and an anode of theconditioner capacitor; an anode of the trigger zener diode, a first endof the trigger resistor and an anode of the trigger capacitor areconnected; a cathode of the trigger capacitor is connected to theground; a second end of the trigger resistor is connected to a base ofthe trigger transistor; an emitter of the trigger transistor isconnected to the drive section; the drive section is comprised of afirst drive resistor, a second drive resistor, a third drive resistor, adrive capacitor, a drive diode, and a drive MOSFET; a first end of thesecond drive resistor receives current from the emitter of the triggertransistor; a second end of the third drive resistor is connected to theground; a second end of the second drive resistor and a first end of thethird drive resistor are connected; the second drive resistor and thethird drive resistor comprise a drive voltage divider between theemitter of the trigger transistor and the ground; an anode of the drivecapacitor is connected to the second end of the second drive resistor,the first end of the third drive resistor, and a gate of the driveMOSFET; a source of the drive MOSFET is connected to the ground and adrain of the drive MOSFET is connected to a cathode of the drive diode;an anode of drive diode is connected to a second end of the first driveresistor, and a first end of the first drive resistor is connected tothe disable section; and the disable section is comprised of a disableresistive element, a disable resistor, a disable capacitor, a disableresistive element, and a disable TRIAC; a second end of the disableresistor, a cathode of the disable capacitor, and a gate of the disableTRIAC are connected to the first end of the first drive resistor; afirst end of the disable resistor, an anode of the disable capacitor, asecond end of a disable resistive element, and a main terminal 1 (MT1)of the disable TRIAC are connectable to the first end of the coil; amain terminal 2 (MT2) of the disable TRIAC is connected to the ground; afirst of end of the disable resistive element is connectable to thealternator.

In yet another aspect of an embodiment of the invention, a piece ofoutdoor power equipment comprises an alternator, an engine, and analternator overvoltage protection circuit; the alternator is connectedto the engine; the alternator overvoltage protection circuit comprisinga conditioner section, a trigger section, a drive section, and a disablesection; the conditioner section is connected to the alternator rotatedby the engine of the piece of outdoor power equipment, and the disablesection is electrically connected to a load; the trigger section islocated between and electrically connected to the conditioner sectionand the drive section; the drive section is located between andelectrically connected to the trigger section and the disable section;the conditioner section is configured to condition voltage outputreceived from the alternator, and output the conditioned voltage to thetrigger section; the trigger section is configured to receive theconditioned voltage from the conditioner section; the trigger section isfurther configured to output current to the drive section when thealternator output voltage exceeds an alternator overvoltage threshold,wherein the trigger section does not output current to the drive sectionwhen the alternator output voltage does not exceed the alternatorovervoltage threshold; the drive section is configured to activate thedisable section when the drive section receives current from the triggersection; and the disable section is configured to divert at least aportion of current away from the load to a ground of the alternatorovervoltage protection circuit through a low impedance path when thedisable section is activated, thereby disabling the engine.

In another aspect of the invention, the load is a coil of an enginecomponent, the disable section is configured to divert at least aportion of current away from the coil to a ground of the alternatorovervoltage protection circuit through a low impedance path when thedisable section is activated, wherein diverting a portion of currentaway from the coil to a ground either causes the coil to drop out orcauses a fuse to blow in a disable resistive element that delivers powerto the coil, thereby disabling the engine.

In a further aspect of the invention, the load is a magneto connected toand configured to supply spark to the engine; wherein the disablesection is configured to divert at least a portion of current away fromthe magneto to a ground of the alternator overvoltage protection circuitthrough a low impedance path when the disable section is activated,thereby removing spark from and disabling the engine.

In a further aspect of the invention, the coil is a fuel solenoid coil,air intake valve coil, and/or a fuel pump relay coil.

In yet another aspect of an embodiment of the invention, a method ofprotecting a piece of outdoor power equipment in an overvoltagecondition, the method comprising providing a piece of outdoor powerequipment comprising an alternator overvoltage protection circuit,wherein the alternator overvoltage protection circuit comprises aconditioner section, a trigger section, a drive section, and a disablesection; the conditioner section is connected to an alternator having anoutput voltage rotated by an engine of the piece of outdoor powerequipment, and the disable section is electrically connected to a load;the trigger section is located between and electrically connected to theconditioner section and the drive section; the drive section is locatedbetween and electrically connected to the trigger section and thedisable section; conditioning the voltage output received from thealternator using the conditioner section, and providing the conditionedvoltage to the trigger section; receiving the conditioned voltage withthe trigger section from the conditioner section; outputting currentfrom the trigger section to the drive section when the alternator outputvoltage exceeds an alternator overvoltage threshold, wherein the triggersection does not output current to the drive section when the alternatoroutput voltage does not exceed the alternator overvoltage threshold;activating the disable section using the drive section when the drivesection receives current from the trigger section; and wherein thedisable section is configured to divert at least a portion of currentaway from the load to a ground of the alternator overvoltage protectioncircuit, thereby disabling the engine; wherein the portion of currentdiverted away from the load travels to ground through a low impedancepath.

In another aspect of the invention, the load is a coil of an enginecomponent, the disable section diverts at least a portion of currentaway from the coil to a ground of the alternator overvoltage protectioncircuit through a low impedance path when the disable section isactivated, wherein diverting a portion of current away from the coil tothe ground either causes the coil to drop out or causes a fuse to blowin a disable resistive element that delivers power to the coil, therebydisabling the engine.

In a further aspect of the invention, the coil is a fuel solenoid coil,air intake valve coil, and/or a fuel pump relay coil.

In a further aspect of the invention, the load is a magneto connected toand configured to supply spark to the engine; wherein the disablesection diverts at least a portion of current away from the magneto tothe ground of the alternator overvoltage protection circuit through alow impedance path when the disable section is activated, therebyremoving spark from and disabling the engine.

In yet another aspect of an embodiment of the invention, an alternatorovervoltage protection circuit comprises a conditioner section, atrigger section, a drive section, and a disable section; the conditionersection is connectable to an alternator rotated by an engine, and thedisable section is connectable to a load; the trigger section is locatedbetween and electrically connected to the conditioner section and thedrive section; the drive section is located between and electricallyconnected to the trigger section and the disable section; the load is anengine control module (ECM) connected to and configured to control theoperation of the engine; the conditioner section is configured tocondition voltage output received from the alternator, and output theconditioned voltage to the trigger section; the trigger section isconfigured to receive the conditioned voltage from the conditionersection; the trigger section is further configured to output current tothe drive section when the alternator output voltage exceeds analternator overvoltage threshold, wherein the trigger section does notoutput current to the drive section when the alternator output voltagedoes not exceed the alternator overvoltage threshold; the drive sectionis configured to activate the disable section when the drive sectionreceives current from the trigger section; and the disable section isconfigured to divert at least a portion of current away from the ECM toa ground of the alternator overvoltage protection circuit through a lowimpedance path when the disable section is activated, thereby groundinga kill pin of the ECM and disabling the engine.

In another aspect of the invention, the disable section comprises adisable TRIAC having a main terminal 1 (MT1) connected to the ECM and amain terminal 2 (MT2) connected to the ground, wherein the disable TRIACis configured to conduct when the disable section is activated, therebycreating a first current path between the ECM at the MT1 and the groundat the MT2.

In a further aspect of the invention, the disable TRIAC is configured totrigger and conduct in quadrant 3.

In another aspect of the invention, the drive section activates thedisable section by creating a low impedance path through the drivesection between the ECM and the ground, the low impedance path betweenthe ECM and the ground creates a second current path and a third currentpath; the third current path uses a portion of current provided by theECM to produce a voltage at a gate of the disable TRIAC, the secondcurrent path removes current from the gate of the disable TRIAC, therebycausing disable TRIAC to conduct, wherein the voltage produced at thegate of the disable TRIAC and the current removed from the gate of thedisable TRIAC are sufficient for the disable TRIAC to trigger andconduct in quadrant 3.

In a further aspect of the invention, the low impedance path created bythe drive section is comprised of a drive MOSFET; the drive MOSFET isconfigured to transition from a high impedance state to a low impedancestate when the trigger section provides current to the drive section;wherein the current provided from the trigger section to the drivesection flows through a drive voltage divider in the drive section,which produces a voltage at a gate of the drive MOSFET sufficient forthe path between a drain and a source of the drive MOSFET to transitionfrom high impedance state to a low impedance state.

In another aspect of the invention, the drive voltage divider isconfigured to charge a drive capacitor of the drive section, wherein thedrive capacitor is connected to the gate of the drive MOSFET andcontains sufficient charge to maintain the drive MOSFET in the lowimpedance state for a few seconds after the engine stops rotating.

In a further aspect of the invention, the trigger section is comprisedof a trigger transistor configured to receive current from thealternator through the conditioner section, the trigger transistor isfurther configured to provide current to the drive voltage divider whenthe alternator output voltage exceeds the alternator overvoltagethreshold.

In another aspect of the invention, the alternator overvoltage thresholdis about 15 VDC.

In a further aspect of the invention, the alternator overvoltagethreshold is about 18.65 VDC.

In another aspect of the invention, the alternator overvoltage thresholdis about 20 VDC.

In a further aspect of the invention, the conditioner section iscomprised of a conditioner diode, a conditioner resistor, a conditionerzener diode, and a conditioner capacitor; an anode of the conditionerdiode receives the voltage output from the alternator; a first end ofthe conditioner resistor is connected to a cathode of the conditionerdiode and a second end of the conditioner resistor is connected to thetrigger section, the conditioner zener diode and the conditionercapacitor are connected in parallel, a cathode of the conditioner zenerdiode and an anode of the conditioner capacitor are connected to thesecond end of the conditioner resistor; an anode of the conditionerzener diode and a cathode of the conditioner capacitor are connected tothe ground; the trigger section is comprised of a trigger zener diode, atrigger capacitor, a trigger resistor, and a trigger transistor; acathode of the trigger zener diode and a collector of the triggertransistor are connected to a second end of the conditioner resistor,the cathode of the conditioner zener diode, and the anode of theconditioner capacitor; an anode of the trigger zener diode, a first endof the trigger resistor and an anode of the trigger capacitor areconnected; a cathode of the trigger capacitor is connected to theground; a second end of the trigger resistor is connected to a base ofthe trigger transistor; an emitter of the trigger transistor isconnected to the drive section; the drive section is comprised of afirst drive resistor, a second drive resistor, a third drive resistor, adrive capacitor, a drive diode, and a drive MOSFET; a first end of thesecond drive resistor receives current from the emitter of the triggertransistor; a second end of the third drive resistor is connected to theground; a second end of the second drive resistor and a first end of thethird drive resistor are connected; the second drive resistor and thethird drive resistor comprise a drive voltage divider between theemitter of the trigger transistor and the ground; an anode of the drivecapacitor is connected to the second end of the second drive resistor,the first end of the third drive resistor, and a gate of the driveMOSFET; a source of the drive MOSFET is connected to the ground and adrain of the drive MOSFET is connected to a cathode of the drive diode;an anode of drive diode is connected to a second end of the first driveresistor, and a first end of the first drive resistor is connected tothe disable section; and the disable section is comprised of a disableresistor, a disable capacitor, and a disable TRIAC; a second end of thedisable resistor, a cathode of the disable capacitor, and a gate of thedisable TRIAC are connected to the first end of the first driveresistor; a first end of the disable resistor, an anode of the disablecapacitor, and a main terminal 1 (MT1) of the disable TRIAC areconnectable to the ECM; a main terminal 2 (MT2) of the disable TRIAC isconnected to the ground.

Advantages of the present invention will become more apparent to thoseskilled in the art from the following description of the embodiments ofthe invention which have been shown and described by way ofillustration. As will be realized, the invention is capable of other anddifferent embodiments, and its details are capable of modification invarious respects.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

These and other features of the present invention, and their advantages,are illustrated specifically in embodiments of the invention now to bedescribed, by way of example, with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a block diagram of an alternator overvoltage protectioncircuit in accordance with an exemplary embodiment of the invention;

FIG. 2 is a piece of outdoor power equipment in accordance with anexemplary embodiment of the invention;

FIGS. 3-5 are block diagrams of an alternator overvoltage protectioncircuit in a piece of outdoor power equipment in accordance with anexemplary embodiment of the invention;

FIGS. 6A-D are schematics of an alternator overvoltage protectioncircuit in accordance with an exemplary embodiment of the invention;

FIGS. 7A-D are schematics of an alternator overvoltage protectioncircuit in accordance with an exemplary embodiment of the invention;

FIG. 8 is a block diagram of an alternator overvoltage protectioncircuit in a piece of outdoor power equipment in accordance with anexemplary embodiment of the invention; and

FIGS. 9A-D are schematics of an alternator overvoltage protectioncircuit in accordance with an exemplary embodiment of the invention.

It should be noted that all the drawings are diagrammatic and not drawnto scale. Relative dimensions and proportions of parts of these figureshave been shown exaggerated or reduced in size for the sake of clarityand convenience in the drawings. The same reference numbers aregenerally used to refer to corresponding or similar features in thedifferent embodiments. Accordingly, the drawing(s) and description areto be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, is not limited to the precise valuespecified. In at least some instances, the approximating language maycorrespond to the precision of an instrument for measuring the value.Range limitations may be combined and/or interchanged, and such rangesare identified and include all the sub-ranges stated herein unlesscontext or language indicates otherwise. Other than in the operatingexamples or where otherwise indicated, all numbers or expressionsreferring to quantities of ingredients, reaction conditions and thelike, used in the specification and the claims, are to be understood asmodified in all instances by the term “about”.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, or that the subsequentlyidentified material may or may not be present, and that the descriptionincludes instances where the event or circumstance occurs or where thematerial is present, and instances where the event or circumstance doesnot occur or the material is not present.

As used herein, the terms “comprises”, “comprising”, “includes”,“including”, “has”, “having”, or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article or apparatus that comprises a list of elements is notnecessarily limited to only those elements, but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

The singular forms “a”, “an”, and “the” include plural referents unlessthe context clearly dictates otherwise.

Referring to FIGS. 1-5, an alternator overvoltage protection circuit 30for a piece of outdoor power equipment 10 is shown in accordance with anexemplary embodiment. The overvoltage protection circuit 30 is designedto disable the engine 20 of a piece of outdoor power equipment 10 in theevent that the voltage output of alternator 21 of engine 20 exceeds acertain threshold voltage. It is contemplated that overvoltageprotection circuit 30 can be used with any piece of outdoor powerequipment 10 that has an engine 20 with an alternator 21, such as, butnot limited to, a riding lawn mower, a zero turn mower, or a gardentractor.

Under typical operating conditions, the voltage output of alternator 21is typically regulated by battery 90, and charges battery 90 andprovides DC voltage to other loads in the range of about 12-15 volts.

Excessive overvoltage of the output of alternator 21 can occur by suddenloss of connection to battery 90. Further, excessive overvoltage of theoutput of alternator 21 can also occur when a piece of outdoor powerequipment 10 with a failed or damaged (e.g. sulfated) battery 90 is jumpstarted from an external source, and the source is then removed afterengine 20 is operating, thereby rotating alternator 21, which isoutputting voltage that is unable to be regulated by the failed ordamaged battery 90.

An excessive overvoltage, overvoltage event, or alternator overvoltagecondition is defined as when the output voltage of alternator 21 exceedsan alternator overvoltage threshold. A non-excessive overvoltage,non-overvoltage event, or non-alternator overvoltage condition isdefined as when the output voltage of alternator 21 does not exceed analternator overvoltage threshold.

Referring to FIG. 1, a block diagram of the overvoltage protectioncircuit 30 in accordance with an exemplary embodiment is shown. Theovervoltage protection circuit 30 includes a conditioner section 40,trigger section 50, drive section 60, and disable section 70. In someembodiments, conditioner section 40 has an conditioner section input 41and a conditioner section output 49, trigger section 50 has a triggersection input 51 and a trigger section output 59, drive section 60 has adrive section input 61 and a drive disable section interface 69, anddisable section 70 has a load interface 71 and a disable section output79.

Conditioner section 40 receives voltage from alternator 21 and thevoltage received from alternator 21 is filtered, rectified, and bufferedto reduce transients. After the voltage is filtered, rectified, andbuffered, it is then passed from the conditioner section 40 to triggersection 50. The trigger section 50 passes current to drive section 60when the output voltage of alternator 21 exceeds an alternatorovervoltage threshold. In one embodiment, the alternator overvoltagethreshold is 15 VDC. In another embodiment, the alternator overvoltagethreshold is 20 VDC. In yet another embodiment, the alternatorovervoltage threshold is 18.65 VDC.

When current is provided to drive section 60 by trigger section 50,drive section 60 activates disable section 70. Disable section 70 drawscurrent away from load 80, thereby disabling load 80. In someembodiments, load 80 is a magneto 22 on engine 20. In other embodiments,load 80 is a coil 23 for a component of engine 20 whose function isnecessary for combustion to take place in the engine 20 and thecomponent only allows combustion to take place when voltage is suppliedto coil 23, such as a fuel pump relay coil or fuel solenoid coil. Forembodiments in which coil 23 is a fuel pump relay coil or a fuelsolenoid coil, the delivery of fuel to engine 20 is cut off when voltageis removed from coil 23. Thereby, removing voltage from coil 23 disablesengine 20.

Accordingly, when disable section 70 draws current away from load 80,engine 20 stops rotating. Therefore, the voltage output of alternator 21rotated by engine 20 also ceases, thereby removing the alternatorovervoltage condition.

Referring to FIG. 2, a piece of outdoor power equipment 10 is shownwhich contains, or is capable of being equipped with an alternatorovervoltage protection circuit 30.

Turning to FIGS. 3-5 and 8, FIG. 3 shows a block diagram of alternatorovervoltage protection circuit 30 is shown in relation to battery 90,engine 20 of a piece of outdoor power equipment 10, alternator 21 andload 80 in accordance with an exemplary embodiment. As can be seen,alternator 21 and load 80 are connected to engine 20. Further,overvoltage protection circuit 30 is electrically connected and/orconnectable to alternator 21 and load 80. Battery 90 is connected toalternator 21. In some embodiments, conditioner section 40 has anconditioner section input 41 and a conditioner section output 49,trigger section 50 has a trigger section input 51 and a trigger sectionoutput 59, drive section 60 has a drive section input 61 and a drivedisable section interface 69, and disable section 70 has a loadinterface 71 and a disable section output 79. As can be seen in FIGS.4-5 and 8, in some embodiments, load 80 is magneto 22, in furtherembodiments, load 80 is engine control module 26, and in otherembodiments, load 80 is coil 23.

Turning to FIG. 4 discussed above and FIGS. 6A-D, a schematic view of anembodiment of overvoltage protection circuit 30, this embodiment ofovervoltage protection circuit 30 is designed to function with apositive pulse magneto 22 as the load 80. As can be seen, theconditioner section 40 includes conditioner section input 41,conditioner diode D1, conditioner resistor R2, conditioner zener diodeD2, conditioner capacitor C3, and conditioner section output 49.Conditioner section input 41 connected to the output of alternator 21and receives voltage output from alternator 21. In some embodiments, theanode of conditioner diode D1 is conditioner section input 41. A firstend 42 of conditioner resistor R2 is connected to the cathode ofconditioner diode D1. Conditioner zener diode D2 and conditionercapacitor C3 are connected in parallel, with the cathode of conditionerzener diode D2 and the anode of conditioner capacitor C3 being connectedto the second end 43 of conditioner resistor R2 and the anode ofconditioner zener diode D2 and the cathode of conditioner capacitor C3being connected to ground.

Conditioner diode D1 rectifies the voltage output of alternator 21 toprevent backflow of current when an overvoltage of alternator 21 occursand overvoltage protection circuit 30 begins to actively disable engine20, thereby decreasing the voltage output of alternator 21. Conditionerresistor R2 and conditioner capacitor C3 filter the voltage output ofalternator 21 provided to conditioner section 40 to prevent falsetriggering of trigger section 50, due to short duration transientvoltages that may otherwise exceed the alternator overvoltage thresholdof the overvoltage protection circuit 30 and disable TRIAC Q2 to conductand draw current away from load 80. Conditioner zener diode D2 acts as asnubber to clamp an overvoltage condition to protect trigger transistorQ1.

In one embodiment, the conditioner section output 49 is comprised of thesecond end of conditioner resistor R2, the anode of conditionercapacitor C3, and the cathode of conditioner zener diode D2 and providesconditioned voltage to the trigger section input 51. As can be seen,conditioner section 40 is configured to condition voltage outputreceived from alternator 21, and output conditioned voltage to triggersection 50.

Trigger section 50 includes trigger section input 51, trigger zenerdiode D3, trigger capacitor C4, trigger resistor R5, trigger transistorQ1, and trigger section output 59. In one embodiment, the cathode oftrigger zener diode D3 and the collector of trigger transistor Q1comprise to trigger section input 51. The anode of trigger zener diodeD3, first end 52 of trigger resistor R5 and anode of trigger capacitorC4 are connected. The cathode of trigger capacitor C4 is connected toground. The second end 53 of trigger resistor R5 is connected to thebase of trigger transistor Q1. It is contemplated that in someembodiments, a second base resistor is present between trigger resistorR5 and the base of trigger transistor Q1. Further, it is contemplatedthat in some embodiments, a resistor is present between the base andemitter of trigger transistor Q1.

In operation, when the alternator overvoltage threshold is exceeded bythe output voltage of alternator 21, trigger zener diode D3 becomesreverse biased and causes trigger capacitor C4 to charge. When triggercapacitor C4, trigger transistor Q1 begins to conduct and amplifies thecurrent passing through trigger zener diode D3. In one embodiment,trigger transistor Q1 begins to conduct when trigger capacitor C4 ischarged to 0.65V. It is contemplated that in some embodiments, triggertransistor Q1 can be a PNP transistor, and in other embodiments, triggertransistor Q1 can be an NPN transistor. This amplified current passesthrough the collector of trigger transistor Q1 to drive section 60. Inone embodiment, the emitter of trigger transistor Q1 comprises triggersection output 59.

Drive section 60 includes drive section input 61, drive disable sectioninterface 69, first drive resistor R3, second drive resistor R4, thirddrive resistor R7, drive capacitor C5, drive diode D4, and drivemetal-oxide-semiconductor field-effect-transistor (MOSFET) Q3. DriveMOSFET Q3 is an N-channel MOSFET. In one embodiment, the first end 64 ofsecond drive resistor R4 comprises drive section input 61. The secondend 67 of third drive resistor R7 is connected to ground. Second end 65of second drive resistor R4 and first end 66 of third drive resistor R7are connected. Accordingly, second drive resistor R4 and third driveresistor R7 act as a drive voltage divider 68 between drive sectioninput 61 and ground. Further, the anode of drive capacitor C5 isconnected to second end 65 of second drive resistor R4, first end 66 ofthird drive resistor R7, and gate of drive MOSFET Q3. The source ofdrive MOSFET Q3 is connected to ground and the drain of drive MOSFET Q3is connected to the cathode of drive diode D4. The anode of drive diodeD4 is connected to a second end 63 of first drive resistor R3. In oneembodiment, the first end 62 of first drive resistor R3 comprises thedrive disable section interface 69 that receives current from disablesection output 79 of disable section 70.

The embodiment of disable section 70 shown in FIGS. 6A-D has a loadinterface 71, disable section output 79, disable resistor R1, disablecapacitor C1, and disable triode for alternating current (TRIAC) Q2. Inthis embodiment, disable section output 79 sends current to drivedisable section interface 69 of drive section 60. In one embodiment, thesecond end 73 of disable resistor R1, cathode of disable capacitor C1,and gate of disable TRIAC Q2 are connected to comprise disable sectionoutput 79. In one embodiment, the first end 72 of disable resistor R1,anode of disable capacitor C1, and main terminal 1 (MT1) of disableTRIAC Q2 are connected to comprise load interface 71, which is connectedto and receives power from magneto 22. Main terminal 2 (MT2) of disableTRIAC Q2 is connected to ground. Disable capacitor C1 filters transientsto prevent false triggering of the gate of disable TRIAC Q2.

In operation, the current travelling through and exiting the emitter oftrigger transistor Q1 imposes a voltage at gate of drive MOSFET Q3. Morespecifically, the current travelling through and exiting the emitter oftrigger transistor Q1 travels through the drive voltage divider 68comprised of second drive resistor R4 and third drive resistor R7. Drivevoltage divider 68 imposes a voltage at the high impedance gate of driveMOSFET Q3 sufficient to cause drive MOSFET Q3 to conduct. Gate of driveMOSFET Q3 is located between second drive resistor R4 and third driveresistor R7.

Drive MOSFET Q3 normally has a high impedance path between drain andsource, which does not allow current to pass between the drain andsource of drive MOSFET Q3. However, when sufficient voltage is appliedto gate of drive MOSFET Q3, the impedance of the path between drain andsource becomes low, thereby allowing a third portion of the currentgenerated by magneto 22 to be directed or diverted away from magneto 22and flow along third current path 76 when magneto 22 produces a positivepulse. Third current path 76 is comprised of disable resistor R1, firstdrive resistor R3, dive diode D4, and drive MOSFET Q3. Further, disableresistor R1 and first drive resistor R3 of third current path 76 form athird current path voltage divider, with the gate of disable TRIAC Q2connected between disable resistor R1 and first drive resistor R3. Itcan be seen that a node is formed by the second end 73 of disableresistor R1, first end 62 of first drive resistor R3, gate of disableTRIAC Q2, and cathode of disable capacitor C1.

Disable TRIAC Q2 is normally a high impedance path between terminal MT1and MT2 when not triggered and not conducting. However, disable TRIAC Q2acts as a low impedance path between MT1 and MT2 when triggered andconducting, thereby grounding current produced by magneto 22.Accordingly, when a third portion of the current generated by a positivevoltage pulse of magneto 22 flows along third current path 76, a voltageis produced at the gate of disable TRIAC Q2 sufficient to trigger thegate of disable TRIAC Q2. Further, the voltage produced at the gate ofdisable TRIAC Q2 is less than the voltage at MT1 of disable TRIAC Q2,due to third current path voltage divider formed by disable resistor R1and drive resistor R3, and the voltage at grounded MT2 of disable TRIACQ2 is less than the voltage at gate and MT1 of disable TRIAC Q2, whichresults in disable TRIAC Q2 conducting in quadrant 3.

When disable TRIAC Q2 conducts in quadrant 3, a second portion ofcurrent travels along a second current path 75 from magneto 22 toground. The second current path 75 from magneto 22 to ground iscomprised disable TRIAC Q2, first drive resistor R3, drive diode D4, anddrive MOSFET Q3. Current travelling along the second current path 75exits magneto 22, enters disable TRIAC Q2 at MT1, exits disable TRIAC Q2at gate, travels through first drive resistor R3 and drive diode D4,enters the drain of drive MOSFET Q3, and exits from the source of driveMOSFET Q3 to ground.

Current travelling along second current path 75 through disable TRIAC Q2from MT1 to gate while disable TRIAC Q2 is operating in quadrant 3causes disable TRIAC Q2 to conduct, thereby creating a first currentpath 74 from magneto 22 to ground for a first portion of current frommagneto 22. First current path 74 from magneto 22 to ground is comprisedof disable TRIAC Q2. Current travelling along the first current path 74exits magneto 22, enters disable TRIAC Q2 at MT1, and exits MT2 ofdisable TRIAC Q2 at MT2 to ground. It is understood that when disableTRIAC Q2 is conducting, only a small amount of current produced bymagneto 22 travels along third current path 76 and second current path75, while the majority of the current produced by magneto 22 travelsalong the first current path 74, which is a low impedance path frommagneto 22 to ground through conducting disable TRIAC Q2.

Removing current from magneto 22 through first current path 74 usingdisable TRIAC Q2 removes current from the circuit of magneto 22, therebydisabling the source of spark for engine 20 and stopping engine 20 ofoutdoor power equipment 10. Because drive MOSFET Q3 has a high inputresistance, once disable TRIAC Q2 begins conducting, disable TRIAC Q2remains in a state of continuous conduction for sufficient duration todisable engine 20.

As can be seen, while engine 20 is stopping, the output of alternator 21is reduced and disable TRIAC Q2 is held in low impendence until thecharge in drive capacitor C5 is discharged through third drive resistorR7, which causes the voltage at the gate of drive MOSFET Q3 to fallbelow the threshold voltage of drive MOSFET Q3 and drive MOSFET Q3 stopsconducting.

In one embodiment, the charge on drive capacitor C5 falls below thethreshold voltage of drive MOSET Q3 a few seconds after engine 20 stopsrotating.

Stated alternatively, an alternator overvoltage protection circuit 30comprises a TRIAC and a MOSFET, wherein TRIAC is disable TRIAC Q2 andMOSFET is drive MOSFET Q3. The TRIAC is electrically connected to theMOSFET and the TRIAC is electrically connected to magneto 22. The TRIACis configured to ground the magneto 22 when triggered by the MOSFET.Further, the MOSFET is electrically connected to alternator 21. TheMOSFET is configured to conduct when the alternator operates in anovervoltage condition such as when the output voltage of alternator 21exceeds an alternator overvoltage threshold.

Further, alternator 21 is connected to and rotated by engine 20.Additionally, the magneto 22 is connected to and provides spark to theengine 20. Accordingly, grounding the magneto 22 with the TRIAC disablesthe magneto 22 and stops the voltage output from the alternator 21.

In some embodiments, the alternator overvoltage protection circuit 30further comprises a transistor, wherein the transistor is triggertransistor Q1. The transistor is electrically connected to thealternator 21 and configured to conduct when the alternator 21 operatesin the overvoltage condition.

Turning to FIG. 5 discussed above and FIGS. 7A-D, a schematic view ofanother embodiment of overvoltage protection circuit 30, this embodimentof overvoltage protection circuit 30 is designed to function with a coil23 as the load 80. In some embodiments, coil 23 is a fuel pump relaycoil for the fuel pump providing fuel to engine 20 of outdoor powerequipment 10. In other embodiments, coil 23 is the fuel solenoid coilfor the fuel solenoid providing fuel to engine 20 of outdoor powerequipment 10. In further embodiments, coil 23 is an air intake valvecoil for the air intake providing air to engine 20 of outdoor powerequipment 10. However, it is contemplated that the coil 23 can be thecoil of any component of outdoor power equipment 10 that will disablethe combustion in engine 20 when voltage is removed from coil 23, whichwill disable the output of alternator 21 of outdoor power equipment 10.Further, it is contemplated that the coil 23 can be the coil of anycomponent of outdoor power equipment 10 that will disable the combustionin engine 20 when coil 23 is shorted or grounded by disable TRIAC Q2,thereby disabling the output of alternator 21 of outdoor power equipment10.

The conditioner section 40, trigger section 50, and drive section 60contain the same components and are designed to function in the samemanner as described in conjunction with FIG. 4 and FIGS. 6A-D above.However, the configuration and functionality of disable section 70differs between the embodiments shown in FIG. 4 and FIGS. 6A-D ascompared to FIG. 5 and FIGS. 7A-D.

The embodiment of disable section 70 shown in FIG. 5 and FIGS. 7A-D havea load interface 71, disable section output 79, disable resistor R1,disable capacitor C1, disable TRIAC Q2, and a disable resistive elementR8. Load interface 71 connects load 80 to disable section 70. In thisembodiment, load 80 is in the form of coil 23.

A first end 77 of disable resistive element R8 is connected to theoutput of alternator 21 and receives voltage from alternator 21. Asecond end 78 of disable resistive element R8 is connected to MT1 ofdisable TRIAC Q2, anode of disable capacitor C1, and a first end 72 ofdisable resistor R1. Further, a second end 78 of disable resistiveelement R8 is connected to a first end 24 of coil 23, accordingly, coil23 receives power from alternator 21 through disable resistive elementR8. Second end 25 of coil 23 is connected to ground.

Further, in this embodiment, disable section output 79 sends current todrive disable section interface 69 of drive section 60. In oneembodiment, the second end 73 of disable resistor R1, cathode of disablecapacitor C1, and gate of disable TRIAC Q2 are connected to comprisedisable section output 79. Main terminal 2 (MT2) of disable TRIAC Q2 isconnected to ground. Disable capacitor C1 filters transients to preventfalse triggering of the gate of disable TRIAC Q2. In one embodiment, thefirst end 72 of disable resistor R1, anode of disable capacitor C1,second end 78 of disable resistive element R8 and main terminal 1 (MT1)of disable TRIAC Q2 are connected to comprise load interface 71, whichis connected to and provides power to a first end 24 of coil 23.

In operation, the current travelling through and exiting the emitter oftrigger transistor Q1 imposes a voltage at gate of drive MOSFET Q3. Morespecifically, the current travelling through and exiting the emitter oftrigger transistor Q1 travels through the drive voltage divider 68comprised of second drive resistor R4 and third drive resistor R7. Drivevoltage divider 68 imposes a voltage at the high impedance gate of driveMOSFET Q3 sufficient to cause drive MOSFET Q3 to conduct. Gate of driveMOSFET Q3 is located between second drive resistor R4 and third driveresistor R7.

Drive MOSFET Q3 normally has a high impedance path between drain andsource, which does not allow current to pass between the drain andsource of drive MOSFET Q3. However, when sufficient voltage is appliedto gate of drive MOSFET Q3, the impedance of the path between drain andsource becomes low, thereby allowing a third portion of the currentflowing through disable resistive element R8 to be diverted or directedaway from coil 23 and flow along third current path 76. Third currentpath 76 is comprised of disable resistor R1, first drive resistor R3,drive diode D4, and drive MOSFET Q3. Further, disable resistor R1 andfirst drive resistor R3 of third current path 76 form a third currentpath voltage divider, with the gate of disable TRIAC Q2 connectedbetween disable resistor R1 and first drive resistor R3. It can be seenthat a node is formed by the second end 73 of disable resistor R1, firstend 62 of first drive resistor R3, gate of disable TRIAC Q2, and cathodeof disable capacitor C1.

Disable TRIAC Q2 is normally a high impedance path between terminal MT1and MT2 when not triggered and not conducting. However, disable TRIAC Q2acts as a low impedance path between MT1 and MT2 when triggered andconducting, thereby sending to ground current provided through disableresistive element R8, and originally intended to flow through coil 23.Accordingly, when a third portion of the current delivered throughdisable resistive element R8 flows along third current path 76, avoltage is produced at the gate of disable TRIAC Q2 sufficient totrigger the gate of disable TRIAC Q2. Further, the voltage produced atthe gate of disable TRIAC Q2 is less than the voltage at MT1 of disableTRIAC Q2, due to third current path voltage divider formed by disableresistor R1 and first drive resistor R3, and the voltage at grounded MT2of disable TRIAC Q2 is less than the voltage at gate and MT1 of disableTRIAC Q2, which results in disable TRIAC Q2 conducting in quadrant 3.

When disable TRIAC Q2 conducts in quadrant 3, a second portion ofcurrent is directed or diverted away from coil 23 and travels along asecond current path 75 from disable resistive element R8 to ground. Thesecond current path 75 from disable resistive element R8 to ground iscomprised disable TRIAC Q2, first drive resistor R3, drive diode D4, anddrive MOSFET Q3. Current travelling along the second current path 75exits disable resistive element R8, enters disable TRIAC Q2 at MT1,exits disable TRIAC Q2 at gate, travels through first drive resistor R3and drive diode D4, enters the drain of drive MOSFET Q3, and exits thesource of drive MOSFET Q3 to ground.

Current travelling along second current path 75 through disable TRIAC Q2from MT1 to gate while operating in quadrant 3 causes disable TRIAC Q2to conduct, thereby creating a first current path 74 from disableresistive element R8 to ground for a first portion of current directedor diverted away from coil 23. First current path 74 from disableresistive element R8 to ground is comprised of disable TRIAC Q2. Currenttravelling along the first current path 74 exits disable resistiveelement R8, enters disable TRIAC Q2 at MT1, and exits MT2 of disableTRIAC Q2 at MT2 to ground. As can be seen, first current path 74 is inparallel with coil 23. It is understood that when disable TRIAC Q2 isconducting, only a small amount of current delivered by disableresistive element R8 travels along third current path 76 and secondcurrent path 75, while the majority of the current delivered throughdisable resistive element R8 travels along the first current path 74,which is a low impedance path from disable resistive element R8 toground through conducting disable TRIAC Q2. Also, it is understood thatin some embodiments, a small amount of current may continue to flowthrough coil 23 while current is flowing through the third current path76, second current path 75, and first current path 74.

As one can see, the first current path 74 is a low impedance path fromdisable resistive element R8 to ground through conducting disable TRIACQ2. When first current path 74 is active during an alternatorovervoltage event the amount of current flowing through disableresistive element R8 is greatly increased, when compared to the amountof current flowing through disable resistive element R8 during anon-overvoltage event when first current path 74 is not active. Statedalternatively, when disable TRIAC Q2 is conducting during an alternatorovervoltage event the amount of current flowing through disableresistive element R8 is greatly increased, when compared to the amountof current flowing through disable resistive element R8 during anon-overvoltage event when disable TRIAC Q2 is not conducting.

In some embodiments, disable resistive element R8 is a fuse. In otherembodiments, disable resistive element R8 is a resistor. In furtherembodiments, disable resistive element R8 is a fuse and a resistor inseries. Stated alternatively, disable resistive element R8 is comprisedof at least one of a fuse and/or resistor.

In embodiments in which disable resistive element R8 is comprised of afuse, the fuse is sized such that the fuse remains intact during anormal operation of alternator 21, such as during an alternatornon-overvoltage condition of outdoor power equipment 10. However, in theevent of an alternator overvoltage condition, fuse of disable resistiveelement R8 is sized to blow and interrupt the flow of current throughdisable resistive element R8 when disable TRIAC Q2 begins conducting(the first current path 74 is active). When the flow of current throughdisable resistive element R8 is interrupted by the fuse blowing whendisable TRIAC Q2 conducts, the delivery of power to coil 23 is alsointerrupted, thereby disabling engine 20, which will stop the voltageoutput of alternator 21 which is rotated by engine 20. It iscontemplated that in some embodiments, fuse of disable resistive elementR8 is a non-resettable fuse.

It is contemplated that in some embodiments, the fuse of disableresistive element R8 may be a resettable fuse that interrupts thedelivery of power to coil 23 for a sufficient length of time to disableengine 20, which will stop the voltage output of alternator 21 which isrotated by engine 20. Thereby, stopping the output of alternator 21removes the alternator overvoltage condition.

As was stated above, while engine 20 is stopping, the output ofalternator 21 is reduced and disable TRIAC Q2 is held in low impendenceuntil the charge in drive capacitor C5 is discharged through third driveresistor R7, which causes the voltage at the gate of drive MOSFET Q3 tofall below the threshold voltage of drive MOSFET Q3 and drive MOSFET Q3stops conducting.

In one embodiment, the charge on drive capacitor C5 falls below thethreshold voltage of drive MOSET Q3 a few seconds after engine 20 stopsrotating.

In embodiments in which a fuse is not present in disable resistiveelement R8, such as when only a resistor is present, the value of theresistance of disable resistive element R8 is such that coil 23 isprovided with sufficient voltage during normal operation of alternator,such as during an alternator non-overvoltage condition of outdoor powerequipment 10. However, the value of the resistance of the resistor indisable resistive element R8 is high enough that in the event of analternator overvoltage condition, coil 23 drops out due to aninsufficient voltage drop across coil 23 when disable TRIAC Q2 beginsconducting (the first current path 74 is active). When the disable TRIACQ2 is conducting, a coil dropout voltage divider 82 is formed in whichdisable resistive element R8 acts as the upper resistor 83 in a coildropout voltage divider and elements of third current path 76, secondcurrent path 75, first current path 74, and coil 23 acts in parallel asthe lower resistor 84 of the coil dropout voltage divider.

As was stated above, while engine 20 is stopping, the output ofalternator 21 is reduced and disable TRIAC Q2 is held in low impendenceuntil the charge in drive capacitor C5 is discharged through third driveresistor R7, which causes the voltage at the gate of drive MOSFET Q3 tofall below the threshold voltage of drive MOSFET Q3 and drive MOSFET Q3stops conducting.

In one embodiment, the charge on drive capacitor C5 falls below thethreshold voltage of drive MOSET Q3 a few seconds after engine 20 stopsrotating.

Turning to FIG. 8 discussed above and FIGS. 9A-D, a schematic view ofanother embodiment of overvoltage protection circuit 30, this embodimentof overvoltage protection circuit 30 is designed to function with an ECM26 having a “kill pin” as the load 80. When the kill pin of ECM 26 isgrounded through disable TRIAC Q2, the ECM disables the operation ofengine 20. In some embodiments, ECM 26 is an electronic fuel injectionmodule which controls the providing of fuel to engine 20 of outdoorpower equipment 10. In other embodiments, ECM 26 is a digital sparkadvance module which controls the spark provided to engine 20 of outdoorpower equipment 10. However, it is contemplated that the ECM 26 can beany module that controls the operation of engine 20 and has a “kill pin”that will provide sufficient voltage to trigger and cause disable TRIACQ2 to conduct, and disable the operation of engine 20 when kill pin ofECM 26 is grounded by conducting disable TRIAC Q2, which will disablethe output of alternator 21 of outdoor power equipment 10.

The conditioner section 40, trigger section 50, and drive section 60contain the same components and are designed to function in the samemanner as described in conjunction with FIG. 4 and FIGS. 6A-D above.However, the configuration and functionality of disable section 70differs between the embodiments shown in FIG. 4 and FIGS. 6A-D ascompared to FIG. 8 and FIGS. 9A-D.

The embodiment of disable section 70 shown in FIGS. 9A-D has a loadinterface 71, disable section output 79, disable resistor R1, disablecapacitor C1, and disable TRIAC Q2. In this embodiment, disable sectionoutput 79 sends current to drive disable section interface 69 of drivesection 60. In one embodiment, the second end 73 of disable resistor R1,cathode of disable capacitor C1, and gate of disable TRIAC Q2 areconnected to comprise disable section output 79. In one embodiment, thefirst end 72 of disable resistor R1, anode of disable capacitor C1, andMT1 of disable TRIAC Q2 are connected to comprise load interface 71,which is connected to and receives power from the kill pin of ECM 26.MT2 of disable TRIAC Q2 is connected to ground. Disable capacitor C1filters transients to prevent false triggering of the gate of disableTRIAC Q2.

In operation, the current travelling through and exiting the emitter oftrigger transistor Q1 imposes a voltage at gate of drive MOSFET Q3. Morespecifically, the current travelling through and exiting the emitter oftrigger transistor Q1 travels through the drive voltage divider 68comprised of second drive resistor R4 and third drive resistor R7. Drivevoltage divider 68 imposes a voltage at the high impedance gate of driveMOSFET Q3 sufficient to cause drive MOSFET Q3 to conduct. Gate of driveMOSFET Q3 is located between second drive resistor R4 and third driveresistor R7.

Drive MOSFET Q3 normally has a high impedance path between drain andsource, which does not allow current to pass between the drain andsource of drive MOSFET Q3. However, when sufficient voltage is appliedto gate of drive MOSFET Q3, the impedance of the path between drain andsource becomes low, thereby allowing a third portion of the currentprovided by the kill pin of ECM 26 to be directed or diverted away fromECM 26 and flow along third current path 76. Third current path 76 iscomprised of disable resistor R1, first drive resistor R3, dive diodeD4, and drive MOSFET Q3. Further, disable resistor R1 and first driveresistor R3 of third current path 76 form a third current path voltagedivider, with the gate of disable TRIAC Q2 connected between disableresistor R1 and first drive resistor R3. It can be seen that a node isformed by the second end 73 of disable resistor R1, first end 62 offirst drive resistor R3, gate of disable TRIAC Q2, and cathode ofdisable capacitor C1.

Disable TRIAC Q2 is normally a high impedance path between terminal MT1and MT2 when not triggered and not conducting. However, disable TRIAC Q2acts as a low impedance path between MT1 and MT2 when triggered andconducting, thereby grounding kill pin of ECM 26. Accordingly, when athird portion of the current generated by ECM 26 flows along thirdcurrent path 76, a voltage is produced at the gate of disable TRIAC Q2sufficient to trigger the gate of disable TRIAC Q2. Further, the voltageproduced at the gate of disable TRIAC Q2 is less than the voltage at MT1of disable TRIAC Q2, due to third current path voltage divider formed bydisable resistor R1 and drive resistor R3, and the voltage at groundedMT2 of disable TRIAC Q2 is less than the voltage at gate and MT1 ofdisable TRIAC Q2, which results in disable TRIAC Q2 conducting inquadrant 3.

When disable TRIAC Q2 conducts in quadrant 3, a second portion ofcurrent travels along a second current path 75 from ECM 26 to ground.The second current path 75 from ECM 26 to ground is comprised of disableTRIAC Q2, first drive resistor R3, drive diode D4, and drive MOSFET Q3.Current travelling along the second current path 75 exits ECM 26, entersdisable TRIAC Q2 at MT1, exits disable TRIAC Q2 at gate, travels throughfirst drive resistor R3 and drive diode D4, enters the drain of driveMOSFET Q3, and exits from the source of drive MOSFET Q3 to ground.

Current travelling along second current path 75 through disable TRIAC Q2from MT1 to gate while disable TRIAC Q2 is operating in quadrant 3causes disable TRIAC Q2 to conduct, thereby creating a first currentpath 74 from ECM 26 to ground for a first portion of current from ECM26, thereby grounding the kill pin of ECM 26. First current path 74 fromECM 26 to ground is comprised of disable TRIAC Q2. Current travellingalong the first current path 74 exits ECM 26, enters disable TRIAC Q2 atMT1, and exits MT2 of disable TRIAC Q2 at MT2 to ground. It isunderstood that when disable TRIAC Q2 is conducting, only a small amountof current produced by ECM 26 travels along third current path 76 andsecond current path 75, while the majority of the current produced byECM 26 travels along the first current path 74, which is a low impedancepath from ECM 26 to ground through conducting disable TRIAC Q2.

Removing current from ECM 26 through first current path 74 using disableTRIAC Q2 removes current from the circuit of ECM 26 and grounds the killpin of ECM 26, thereby disabling the source of spark when ECM 26 is adigital spark advance module for engine 20 and stopping engine 20 ofoutdoor power equipment 10, or disabling the supply of fuel when ECM 26is an electronic fuel injection module for engine 20 and stopping engine20 of outdoor power equipment 10. Because drive MOSFET Q3 has a highinput resistance, once disable TRIAC Q2 begins conducting, disable TRIACQ2 remains in a state of continuous conduction for sufficient durationto disable engine 20.

As can be seen, while engine 20 is stopping, the output of alternator 21is reduced and disable TRIAC Q2 is held in low impendence until thecharge in drive capacitor C5 is discharged through third drive resistorR7, which causes the voltage at the gate of drive MOSFET Q3 to fallbelow the threshold voltage of drive MOSFET Q3 and drive MOSFET Q3 stopsconducting.

In one embodiment, the charge on drive capacitor C5 falls below thethreshold voltage of drive MOSET Q3 a few seconds after engine 20 stopsrotating.

Stated alternatively, an alternator overvoltage protection circuit 30comprises a TRIAC and a MOSFET, wherein TRIAC is disable TRIAC Q2 andMOSFET is drive MOSFET Q3. The TRIAC is electrically connected to theMOSFET and the TRIAC is electrically connected to ECM 26. The TRIAC isconfigured to ground the kill pin of ECM 26 when triggered by theMOSFET. Further, the MOSFET is electrically connected to alternator 21.The MOSFET is configured to conduct when the alternator operates in anovervoltage condition such as when the output voltage of alternator 21exceeds an alternator overvoltage threshold.

Further, alternator 21 is connected to and rotated by engine 20.Additionally, the ECM 26 is connected to and provides spark and/or fuelto the engine 20. Accordingly, grounding the kill pin of ECM 26 with theTRIAC disables the engine 20 and stops the voltage output from thealternator 21.

In some embodiments, the alternator overvoltage protection circuit 30further comprises a transistor, wherein the transistor is triggertransistor Q1. The transistor is electrically connected to thealternator 21 and configured to conduct when the alternator 21 operatesin the overvoltage condition.

Also disclosed is a piece of outdoor power equipment 10 having analternator overvoltage protection circuit 30 as described above inconjunction with the discussion of FIGS. 1-9D. The piece of outdoorpower equipment 10 can be any piece of outdoor power equipment 10 thathas an engine 20 with an alternator 21, such as, but not limited to, ariding lawn mower, a zero turn mower, or a garden tractor.

Further disclosed is a method of alternator overvoltage protectioncomprising providing a TRIAC and an alternator 21 rotated by an engine20 having a magneto 22, wherein the alternator 21 outputs a voltage whenrotated by the engine 20. The TRIAC is disable TRIAC Q2 and isconfigured to ground the magneto 22 when the alternator 21 operates inan overvoltage condition, thereby disabling the magneto 22, stopping therotation of the engine 20, and stopping the alternator 21 fromoutputting voltage.

In some embodiments, the method further comprises providing a transistorand a MOSFET, wherein the transistor is trigger transistor Q1 and theMOSFET is drive MOSFET Q3. The transistor is configured to conduct whenthe alternator 21 operates in an overvoltage condition. The MOSFET isconfigured to conduct when a voltage is imposed on a gate of the MOSFETby the conducting transistor. Further, the MOSFET is configured todirect a portion of current from the magneto 22 to trigger a gate of theTRIAC when the MOSFET is conducting, thereby causing the TRIAC toconduct.

Also disclosed is another embodiment of a method of protecting a pieceof outdoor power equipment 10 in an overvoltage condition of alternator21. The method comprises providing a piece of outdoor power equipment 10having an alternator overvoltage protection circuit 30. The alternatorovervoltage protection circuit 30 includes a conditioner section 40, atrigger section 50, a drive section 60, and a disable section 70. Theconditioner section 40 is connected to an alternator 21 having an outputvoltage. Alternator 21 is rotated by an engine 20 of the piece ofoutdoor power equipment 10. The disable section 70 is electricallyconnected to a load 80. The trigger section 50 is located between andelectrically connected to the conditioner section 40 and the drivesection 60. The drive section 60 is located between and electricallyconnected to the trigger section 50 and the disable section 70.

The method further comprises conditioning the voltage output receivedfrom the alternator 21 using the conditioner section 40, and providingthe conditioned voltage to the trigger section 50. The conditionedvoltage is received by the trigger section 50 from the conditionersection 40.

The method further comprises outputting current from the trigger section50 to the drive section 60 when the alternator output voltage exceeds analternator overvoltage threshold. Accordingly, the trigger section 50does not output current to the drive section 60 when the alternatoroutput voltage does not exceed the alternator overvoltage threshold.

The method further includes activating the disable section 70 using thedrive section 60 when the drive section 60 receives current from thetrigger section 50. Additionally, the method further includes,configuring the disable section 70 to divert or direct at least aportion of current away from the load 80 to a ground of the alternatorovervoltage protection circuit 30, thereby disabling the engine 20. Theportion of current diverted away from the load 80 travels to groundthrough a low impedance path of the alternator overvoltage protectioncircuit 30.

In some embodiments of the method, load 80 is a coil 23 of a componentof that needs to receive power in order for engine 20 to operate. Thedisable section 70 diverts or directs at least a portion of current awayfrom the coil 23 to a ground of the alternator overvoltage protectioncircuit 30 through a low impedance path when the disable section 70 isactivated. Diverting or directing a portion of current away from thecoil 23 to the ground either causes the coil 23 to drop out or causes afuse to blow in a disable resistive element R8 that delivers power tothe coil 23, thereby disabling the engine 20.

Further, in other embodiments of the method, the load 80 is a magneto 22connected to and configured to supply spark to the engine 20; whereinthe disable section diverts or directs at least a portion of currentaway from the magneto 22 to the ground of the alternator overvoltageprotection circuit 30 through a low impedance path when the disablesection 70 is activated, thereby removing spark from and disabling theengine 20.

While this invention has been described in conjunction with the specificembodiments described above, it is evident that many alternatives,combinations, modifications and variations are apparent to those skilledin the art. Accordingly, the preferred embodiments of this invention, asset forth above are intended to be illustrative only, and not in alimiting sense. Various changes can be made without departing from thespirit and scope of this invention. Combinations of the aboveembodiments and other embodiments will be apparent to those of skill inthe art upon studying the above description and are intended to beembraced therein. Therefore, the scope of the present invention isdefined by the appended claims, and all devices, processes, and methodsthat come within the meaning of the claims, either literally or byequivalence, are intended to be embraced therein.

What is claimed is:
 1. A method of alternator overvoltage protectioncomprising: providing a TRIAC and an alternator rotated by an enginehaving a magneto, wherein said alternator outputs a voltage when rotatedby said engine; configuring said TRIAC to ground said magneto when saidalternator operates in an overvoltage condition, thereby disabling saidmagneto, stopping the rotation of said engine, and stopping saidalternator from outputting voltage; providing a transistor and a MOSFET;configuring said transistor to conduct when said alternator operates insaid overvoltage condition; configuring said MOSFET to conduct when avoltage is imposed on a gate of said MOSFET by said conductingtransistor; and configuring said MOSFET to direct a portion of currentfrom said magneto to trigger a gate of said TRIAC when said MOSFET isconducting, thereby causing said TRIAC to conduct.
 2. The method ofclaim 1, wherein said overvoltage condition is present when saidalternator output voltage is greater than about 18.65 VDC.
 3. The methodof claim 1, wherein said overvoltage condition is present when saidalternator output voltage is greater than about 15 VDC.
 4. The method ofclaim 1, wherein said overvoltage condition is present when saidalternator output voltage is greater than about 20 VDC.